After you install a new applet in some versions of Ubuntu (gnome) it will not be available in the list until you log-out and login again or if you do not restart your computer. This is bad because you will need to close everything to perform either of these things, however it is safe to kill the gnome-panel process and it will then automatically re-load and all the new applets will be available in the list.

killall gnome-panel

No root/sudo privileges are needed for this command.